ABSTRACT The quality of older adults? closest social ties is a proximal predictor of their mental health. The marital relationship in particular has been deemed a unique and singularly important social relationship. Spouses (which throughout this proposal includes cohabitating partners) can act as a source of support and a source of strain, both of which influence older adults? mental health. However, the pathways through which spousal support and strain each influence older adults? mental health are still poorly understood. Studies that have sought to identify mechanisms focus almost exclusively on psychological mechanisms, with a particularly strong emphasis on loneliness. Researchers have recently proposed sleep as a separate?yet related? mechanism that may further explain links between marital quality and mental health. In line with the NIA?s current strategic direction to illuminate pathways by which psychosocial factors affect older adults? mental health, the overarching purpose of the current proposal is to evaluate the role loneliness and sleep (specifically insomnia symptoms) each play in mediating prospective associations between positive (i.e., spousal support) and negative (i.e., spousal strain) aspects of older adults? marital relationships and depressive symptoms. The proposed research leverages three waves of longitudinal data spanning ten years from the National Social Life, Health, and Aging Project (NSHAP). The NSHAP contains the first set of objective sleep data collected from a nationally representative sample of older adults enabling the examination of subjective (i.e., self-reported) and objective (i.e., actigraphy-measured Wake After Sleep Onset) insomnia symptoms, in addition to loneliness, as mechanisms through which spousal support and strain each influence mental health later in life. Aim 1 will evaluate the role loneliness and insomnia symptoms play in mediating prospective effects of spousal support and strain on older adults? depressive symptoms. Aim 2 will further evaluate the moderating role of pain as a context within which associations between spousal support/strain, loneliness, and sleep are exacerbated. Findings from this project will inform intervention efforts aimed at promoting older adults? mental health by targeting not only their intimate relationships and loneliness, but also their sleep. Existing couple-oriented interventions for sleep disorders largely focus on promoting spouses? education and patients? clinical treatment adherence. Findings from this research will illustrate the degree to which improving marital quality represents an additional means of improving sleep and, in turn, improving (or maintaining) mental health. Hypotheses will be tested with longitudinal structural equation modeling, which increases the scientific rigor of the proposed study through the use of latent variables that improve statistical precision and power. Dr. Marini and her co- investigators, Drs. Lynn Martire and Orfeu Buxton, are uniquely poised to carry out this research given their joint expertise on marital quality, chronic illness, and sleep among older adults.